Method of and apparatus for coating metal articles



p 4, 1956 J. B. BRENNAN 2,761,793

METHOD OF AND APPARATUS FOR COATING METAL. ARTICLES Filed Aug. 2, 1952 IN V EN TOR.

I g VW/W ATTORNEYS.

Patented Sept. 4, 1956 METHOD OF AND APPARATUS FOR COATING METAL ARTICLES Joseph B. Brennan, Cleveland, Ohio Application August 2, 1952, Serial No. 302,403

11 Claims. (Cl. 117-51) This invention relates to a method of and apparatus for coating metal articles, and more particularly to the coating of articles of a relatively high melting point metal such as steel, with a lower melting point metal, such as aluminum, or the like.

For many purposes it is desirable to coat articles formed of steel and similar metals which rust or corrode easily with a coating of a relatively rust and corrosion resistant metal, such as aluminum. It is one of the objects of the present invention to provide a method and apparatus by which coatings of this type can be produced economically and efiectively.

Another object is to provide a method and apparatus in which articles of any desired size or shape can be handled easily and effectively.

Still another object is to provide a method and apparatus in which coating is carried out in a substantially continuous process.

According to one feature of the invention the articles to be coated are carried by baskets which are moved in a continuous series through the coating apparatus to coat articles in the baskets successively.

A further object is to provide a method and apparatus in Which the articles to be coated are first heated to a temperature above the melting point of the coating metal, are then covered with molten coating metal and finally have the excess coating metal drained therefrom.

According to another feature of the invention the molten metal is maintained under vacuum or in an atmosphere of inert gas at a reduced pressure and the baskets are evacuated before the molten metal is supplied thereto.

The above and other objects and features of the invention may be more readily apparent from the following description when read in connection with the accompanying drawing, in which The single figure is a sectional view through a coating apparatus embodying the invention.

According to the method of the present invention articles of ferrous material, such as steel, and of any desired size or shape, are placed in baskets preferably formed of a ceramic or like material which is heat resistant. The baskets are evacuated or are subjected to an inert atmosphere at a reduced pressure and the articles therein are heated to a temperature of at least as great as and preferably slightly higher than the melting point of the coating metal, such as aluminum. The baskets are then filled with molten coating metal so that the articles in the baskets are submerged in the metal and the excess metal is then drained from the baskets while maintaining the articles therein at a temperature above the melting point of the coating metal. Thereafter the articles may be cooled and removed for use.

The drawing illustrates one desirable type of apparatus for carrying out the method including an elongated substantially vertical tube formed of an inert material such as a ceramic, porcelain, graphite, stabilized zirconium oxide or the like. In the form shown, t e tube 10 is vertically arranged and has a smooth cylindrical inner surface provided at various levels therein with ports or openings therethrough for the purpose to appear hereinafter. Surrounding the tube intermediate its ends is a receptacle 11 for molten coating metal indicated at 12, which may be aluminum or any other desired coating material for the metal articles. The molten metal in the container 11 may be maintained in heated molten condition by an inductive coil 13 arranged around the container.

The central major portion of the tube and the molten metal container 11 are enclosed in a housing 14, which may be formed of metal if it is spaced far enough from the induction heating coils or of glass or any other desired non-porous material and which is evacuated through a connection 15 to a vacuum pump or the like. If desired, instead of evacuating the housing a small quantity of inert gas could be circulated constantly therethrough at reduced pressure to maintain an inert atmosphere in the housing.

The lower end of the housing 14 seals against a sleeve 16 which provides an annular space 17 around the central tube 10 communicating therewith through ports 18. The space 17 is connected to the vacuum line 15 by means of a pipe 19 so that it will be evacuated and will evacuate the adjacent portion of the tube through the ports 18. Articles passing through the sleeve 16 are adapted to be heated and for this purpose, as shown, an inductive heating coil 21 is mounted in the sleeve to surround the adjacent portion of the tube 10.

Beneath the sleeve 16 an annular supply chamber 22 is provided into which baskets may be inserted as described hereinafter and which is connected to the pipe 19 to be evacuated thereby. The chamber 22 has an opening in its bottom to receive baskets as indicated at 23 and preferably has guide springs 24 therein to engage the baskets and maintain them in alignment. 1

The upper end of the tube 14 above the housing 14 is provided with a cooling coil 25 and preferably an extension 26 is formed above the top end of the tube carrying a second cooling coil 27. Cooling liquid, such as water, may be circulated through the coils 25 and 27, as indicated by the arrows, to cool the articles after coating thereof.

The baskets 23 are preferably cylindrical in shape and are formed of a material similar to that of the tube 10 to fit with a relatively close sliding fit in the tube 16. Each of the baskets is formed in its side wall with a plurality of openings or ports 28 and preferably has an upwardly coned bottom. Bottom ports 29 connect to the lower outside portions of the upwardly coned bottoms and terminate at the sides of the baskets to drain the excess metal therefrom.

The tube It is formed opposite the molten metal container 11 with ports 31 which will communicate with the openings 28 and 29 in the baskets to permit molten metal to flow from the container into the baskets. Additional ports 32 are provided in the tube it above the level of the container 11 through which excess molten metal can drain from the baskets. The articles in the baskets are maintained above the melting point of the coating metal after passing above the container by means of a high frequency heating coil 33 around the tube 10 at a level above the container.

The heating coil 33 may also serve as a part of a supply heating means for molten metal, as more particularly described and claimed in my copending application, Serial No. 225,949, filed May 12, 1951. As shown, a spiral trough 34 extends from the upper part of the housing 14 within the coil 33 spirally around the tube 10 to terminate at its lower end above the molten metal container 11. A supply pipe 35 extends through the top of the housing 14 and terminates above the top of the trough 34. The troughvmay be divided into a plurality of channels as shown so that molten metal introduced into the upper end of the trough through the pipe 35 will flow downwardly around the trough in the form of a relatively thin layer, and will beheated during such flow by the heating coil33. In this way and because of the vacuum in the housing 14, degassing. and deoxidation of the coating metal is accomplished. I

In operation of the apparatus, a series of baskets 23 are filled with articles to be coated, such bolts, nuts, screws, casting or forgings of various types, or other parts of any desired size or shape. The baskets are introduced in a continuous series through the entrance chamber 22 and are forced upwardly through the tube with the bottom of eachbasket resting on the top of the basket immediately beneath it. As the baskets pass through the entrance chamber 22, the sleeve 16 will be evacuated and the metal articles therein will be inductively heated by the heating coil 21 in the sleeve 16. As the baskets move up further the openings 28 and 29 therein will register with the ports 31 in the tube so that molten metal will flow from the container 11 into the baskets to submerge the articles therein. Since the articles were preheated to a temperature of at least as high as the melting point of the coating metal, the coating metal will adhere readily to the articles and a strongly bonded continuous coating will be formed thereon. As the baskets travel further up, the openings 28 and 29 therein will register with the ports 32 in the tube 10 so that all excess metal will be drained from the articles to leave thereon only a relatively thin coating. It will be noted that the temperature of the articles is maintained above the melting point of the coating metal by the heating coil 33 during draining so that there will be no possibility for globules of coating metal to freeze on the articles. Thus, a uniform continuous coating is left on the articles and all excess coating metal is drained from the baskets back into the container 11. As the baskets continue up through the tube 10, the articles will be cooled by the cooling coils 25 and 27 so that by the time the baskets are discharged from the top of the apparatus, they are cool enough to be handled without difliculty.

It will be apparent that the baskets could move downward through the tube 10 as well as upward, or that the tube couldbe at an angle to the vertical rather than vertical. In all cases, however, it is desirable that the baskets first be evacuated and the articles therein heated before exposure to the molten metal and that the temperature be maintained until excess molten metal is completely drained from the baskets.

While one apparatus for carrying out the invention has been illustrated and described in detail, it will be apparent that many other types of apparatus might occur to those skilled in the art and it is, therefore, not intended that the scope of the invention be limited to the precise construction shown nor otherwise than by the terms of the appended claims.

What is claimed is:

1. Apparatus for coating metal articles with a coating metal having a lower melting point than the articles comprising a receptacle to contain a body of molten coating metal, heating means adjacent to the receptacle to heat the metal therein, guide means to guide articles to be coated along a predetermined path toward and through the receptacle and away from the receptacle, heating means adjacent said path anterior to the receptacle to heat the articles to a temperature above the melting point of the coating metal, heating means adjacent to said path posterior to the/receptacle to maintain the articles heated while excess coating metal is removed therefrom, means enclosing the receptacle and the heating means to maintain them under vacuum during heating thereof and removal of excess metal therefrom, and cooling means adjacent to said path posterior to the last named heating means to cool the articles.

2. Apparatus for coating metal articles with a coating metal having a lower melting point than the articles comprising a receptacle to contain a body of molten coating metal, heating means adjacent to the receptacle to heat the metal therein, a guide .tube passing through the receptacle, article containing baskets fitting slidably in the guide tube to pass therethrough and engaging the guide tube sealingly' to prevent flow of molten metal therebetween, and cooperating ports in the baskets and guide tube to connect the baskets to the receptacle to receive molten metal therefrom in one position of the.

baskets and to connect the baskets to a drain space in another position of the baskets for drainage of excess molten metal therefrom.

3. Apparatus for coating metal articles with a coating metal having a lower melting point than the articles comprising a receptacle to contain a body of molten coating metal, heating means adjacent to the receptacle to heat the metal therein, a guide tube passing through the receptacle, article containing baskets fitting slidably in the guide tube to pass therethrough and engaging the guide tube sealingly to prevent flow of molten metal therebetween, heating means adjacent to the guide tube anterior to the receptacle to heat articles in the basket to a temperature above the melting point of the coating metal, cooperating ports in the baskets and guide tube to connect the baskets in one position thereof to the receptacle to receive molten metal therefrom and to connect the baskets in a second position thereof to a drain space to drain excess molten metal therefrom, heating means adjacent to the guide tube at said second position of the baskets to maintain articles in the baskets heated during drainingthereof, and cooling means adjacent to the guide tube beyond the last named heating means to cool the articles.

4. Apparatus for coating metal articles with a coating metal having a lower melting point than the articles comprising a receptacle to contain a body of molten coating metal, heating means adjacent to the receptacle to heat the metal therein, an evacuated chamber enclosing the receptacle, a guide tube extending through the chamber and the receptacle, article containing baskets fitting slidably in the guide tube to pass therethrough and engaging the guide tube sealingly to prevent flow of molten metal therebctween, and cooperating ports in the baskets to connect the baskets in a first position anterior to the receptacle to a source of vacuum, in a second position to the receptacle to receive molten-metal therefrom, and ma third position to an evacuated drain space to drain excess molten metal from the baskets.

5. The construction of claim 4 including heating means adjacent to the guide tube at the first and third positions of the baskets to heat articles in the baskets before molten coating metal is supplied thereto and to maintain the articles heated while excess metal is drained therefrom.

6. Apparatus for coating metal articles with a coating metal having a lower melting point than the articles comprising an elongated substantially vertical guide tube, a series of article containing baskets fitting slidably in the tube to pass therethrough in end to end relationship, an annular receptacle for molten metal surrounding the guide tube intermediate its ends, and ports in the sides of the baskets and at spaced points in the guide tube to connect the baskets in one position to the receptacle to receive molten metal therefrom and in a second position to the space above the receptacle so that excess metal can flow therefrom into the receptacle.

7. Apparatus for coating metal articles with a coating metal having a lowerv melting point than the articles comprising an elongated substantially vertical guide tube, a series of article containing baskets fitting slidably in the tube to pass therethrough in end to end relationship, an annular receptacle for molten metal surrounding the guide tube intermediate its ends, an evacuated chamber enclosing the receptacle and a portion of the guide tube above the receptacle, ports in the sides of the baskets, and cooperating ports in the guide tube below the receptacle to connect the baskets to a source of vacuum, at the level of the receptacle to supply molten metal to the baskets, and in said portion of the guide tube for drainage of excess metal back into the receptacle.

8. The construction of claim 7 including heating means adjacent to the guide tube below the receptacle to heat articles in the baskets to a temperature at least as great as the melting point of the coating metal, and heating means adjacent to the guide tube above the receptacle to maintain the articles heated during draining of excess molten metal therefrom.

9. The construction of claim 8 in which the guide tube and baskets are formed of non-conducting material and the heating means are induction coils around the guide tube.

10. The method of coating metal articles with a coating metal of a lower melting point than the metal articles comprising heating the metal articles to approximately the melting point of the coating metal, subjecting the heated metal articles to vacuum, covering the heated articles with molten coating metal, removing excess coating metal from the articles while maintaining their temperature at least as high as the melting point of the coating metal and below the melting point of the articles,

maintaining the articles in a vacuum while they are covered with molten coating metal and while removing excess coating metal therefrom, and cooling the articles while maintaining them in a vacuum.

11. The method of coating metal articles with coating metal of a lower melting point than the metal articles, comprising preheating the metal articles under vacuum to approximately the melting point of the coating metal, immersing the so heated articles in molten metal maintained under vacuum, removing excess coating metal from the articles while maintaining their temperature at least as high as the melting point of the coating metal and while maintaining the articles under vacuum, and cooling the article under vacuum so that the coating metal solidifies thereon.

References Cited in the file of this patent UNITED STATES PATENTS 1,343,842 Piersol June 15, 1920 1,512,603 Kasser Oct. 21, 1924 2,216,519 Quarnstrom Oct. 1, 1940 2,223,499 Schon Dec. 3, 1940 2,293,840 Lignian Aug. 25, 1942 2,502,770 Watson Apr. 4, 1950 v FOREIGN PATENTS 390 Great Britain 1858 

11. THE METHOD OF COATING METAL ARTICLES WITH COATING METAL OF A LOWER MELTING POINT THAN THE METAL ARTICLES, COMPRISING PREHEATING THE METAL ARTICLES UNDER VACUUM TO APPROXIMATELY THE MELTING POINT OF THE COATING METAL, IMMERSING THE SO HEATED ARTICLES IN MOLTEN METAL MAINTAINED UNDER VACUUM, REMOVING EXCESS COATING METAL FROM THE ARTICLES WHILE MAINTAINING THEIR TEMPERATURE AT LEAST AS HIGH AS THE MELTING POINT OF THE COATING METAL AND WHILE MAINTAINING THE ARTICLES UNDER VACUUM, AND COOLING THE ARTICLE UNDER VACUUM SO THAT THE COATING METAL SOLIDIFIES THEREON. 